The Strange Science Behind Why Alcohol Burns

If you’ve ever taken a shot of alcohol, you know that it comes with certain unexpected consequences—the surprising heat you feel as the liquid slides down your gullet, for instance.

The folks over at SciShow recently tackled the “why” behind alcohol’s burn, and the answer is surprising. It all starts with a receptor known as VR1, contained in our mouths and throats. High temperature foods trigger VR1, which then tells our nerves and brain what’s going on, and results in a burning sensation.

Capsaicin, found in spicy foods, interacts directly with these receptors, as does alcohol ethanol, though in a different way. Ethanol just makes them more sensitive. Your VR1 receptors activate at about 107°F, but ethanol lowers that to just 93 degrees. See where this is going? Body temperature is normally around 98.6°F, so when you feel that burning sensation, it’s because your body itself is now beyond the threshold for those heat receptors.

As host Hank Green says in the video above: “The next time you take a shot and your eyes start watering, just remember it’s not the booze that’s hot, it’s you”—which just might be the best brainy pickup line of all time.

Don’t ever let people tease you for watering down your whiskey. If they’re true aficionados, they’ll know that adding a splash of water or a few cubes of ice to your drink will actually enhance its natural flavors. But how can something as flavorless as water make a barrel-aged scotch or bourbon taste even better? Chemists think they’ve found the answer.

As The Verge reports, researchers from the Linnæus University Centre for Biomaterials Chemistry in Sweden analyzed the molecular composition of whiskey in the presence of water. We already know that the molecule guaiacol is largely responsible for whiskey’s smoky taste and aroma. Guaiacol bonds to alcohol molecules, which means that in straight whiskey that guaiacol flavor will be fairly evenly distributed throughout the cask. Alcohol is repelled by water, and guaiacol partially so. That means when a splash of water is added to the beverage the alcohol gets pushed to the surface, dragging the guaiacol along with it. Concentrated at the top of the glass, the whiskey’s distinctive taste and scent is in the perfect position to be noticed by the drinker.

According to the team’s experiments, which they laid out in the journal Scientific Reports [PDF], whiskey that’s been diluted down to 40 percent to 45 percent alcohol content will start to show more guaiacol sloshing near the surface. Most commercial whiskey is already diluted before it's bottled, so the drink you order in a bar should fall within this range to begin with. Adding additional water or ice will boost the flavor-enhancing effect even further.

As for just how much water to add, the paper doesn’t specify. Whiskey lovers will just have to conduct some experiments of their own to see which ratios suit their palate.

All yeast breads contain some amount of alcohol. Have you ever smelled a rising loaf of bread or, better yet, smelled the air underneath dough that has been covered while rising? It smells really boozy. And that sweet smell that fresh-baked bread has under the yeast and nutty Maillard reaction notes? Alcohol.

However, during the baking process, most of the alcohol in the dough evaporates into the atmosphere. This is basically the same thing that happens to much of the water in the dough as well. And it’s long been known that bread contains residual alcohol—up to 1.9 percent of it. In the 1920s, the American Chemical Society even had a set of experimenters report on it.

Anecdotally, I’ve also accidentally made really boozy bread by letting a white bread dough rise for too long. The end result was that not enough of the alcohol boiled off, and the darned thing tasted like alcohol. You can also taste alcohol in the doughy bits of underbaked white bread, which I categorically do not recommend you try making.

Putting on my industrial biochemistry hat here, many [people] claim that alcohol is only the product of a “starvation process” on yeast once they run out of oxygen. That’s wrong.

The most common brewers and bread yeasts, of the Saccharomyces genus (and some of the Brettanomyces genus, also used to produce beer), will produce alcohol in both a beer wort
and in bread dough immediately, regardless of aeration. This is actually a surprising result, as it runs counter to what is most efficient for the cell (and, incidentally, the simplistic version of yeast biology that is often taught to home brewers). The expectation would be that the cell would perform aerobic respiration (full conversion of sugar and oxygen to carbon dioxide and water) until oxygen runs out, and only then revert to alcoholic fermentation, which runs without oxygen but produces less energy.

Instead, if a Saccharomyces yeast finds itself in a high-sugar environment, regardless of the presence of air it will start producing ethanol, shunting sugar into the anaerobic respiration pathway while still running the aerobic process in parallel. This phenomenon is known as the Crabtree effect, and is speculated to be an adaptation to suppress competing organisms
in the high-sugar environment because ethanol has antiseptic properties that yeasts are tolerant to but competitors are not. It’s a quirk of Saccharomyces biology that you basically only learn about if you spent a long time doing way too much yeast cell culture … like me.